Certain catalysts are known to catalyze hydrogenation of the carbon-carbon double bonds of diene polymers. An unsaturated bond of a polymer is hydrogenated for the purpose of improving the properties of the polymer. If, however, the inherent properties of the polymer are degraded as a result of the hydrogenation, there is no significance in modifying the polymer by hydrogenation. For example, when modification of a styrene/butadiene random or block copolymer proceeds so far as to hydrogenate the benzene ring of styrene, the polymer will lose its rubber-like properties. In the case of an acrylonitrile/butadiene random or block copolymer, reduction of its nitrile group as a result of hydrogenation will markedly reduce the oil resistance of the copolymer. Accordingly, in so modifying a polymer it is necessary to selectively hydrogenate only the olefinic carbon-carbon double bonds.
Noble metals such as platinum and palladium are frequently used as catalysts in hydrogenation. Since these noble metals are expensive they are used in the smallest possible amounts when performing selective hydrogenations.
An article by H. J. Harwood et al, Diimide as a Reagent for the Hydrogenation of Unsaturated Polymers, Die Makromolekulare Chemie, 163, pages 1-12 (1973), discloses the hydrogenation of various butadiene polymers and of polyisoprene with diimide generated in situ from p-toluenesulfonylhydrazide. The best results were obtained when concentrated polymer solutions were heated with a five-fold excess of p-toluenesulfonylhydrazide.
An article by L. A. Mango and R. W. Lantz, Hydrogenation of Unsaturated Polymers with Diimide, Die Makromolekulare Chemie, 163, pages 13-36 (1973), discloses the homogeneous hydrogenation of a series of unsaturated polymeric substrates with diimide formed from a thermal decomposition of p-toluenesulfonylhydrazide at elevated temperatures (110.degree. to 160.degree. C.) in aromatic solvents.
U.S. Pat. No. 4,337,329, discloses a method for the catalytic hydrogenation of conjugated diene polymers wherein the improvement comprises using a catalyst composed of a porous powdery or granular carrier and supported thereon both palladium and at least one metal selected from the group consisting of the metals of Groups Ia, IIa, IIIa, IIIb, IVa, Va, and VIa of the Periodic Tables, germanium and antimony.
Hydrogenation of polymers has been conventionally accomplished by techniques which require the use of highly reactive chemicals or heterogeneous catalysts, both of which have characteristic handling and application problems. Thus, a procedure which can successfully hydrogenate polymers in the latex form without either restriction should be a significant and useful addition to the techniques now used for polymer hydrogenation. The prior art does not suggest or disclose the process of the present invention wherein carbon-carbon double bonds of an unsaturated polymer are hydrogenated through the addition of an oxidant, a reducing agent and a metal activator to the polymer in the latex form.